وَلَوْ دَرَى لَكَفَاهُ مَا يَرُومُ صُبَابَهْ
If he truly understood, even a small remainder of what he seeks would suffice him.
The earlier ṣabābah denotes intense longing, whereas ṣubābah here refers to a small remainder, such as liquid left in a vessel. A change of vowels changes the sense.
The echo is purposeful: endless craving is set against the idea that a modest portion may be enough.